The description herein relates to semiconductor packages, and more specifically to devices and systems for suppressing noise generated within the semiconductor packages.
In a conventional semiconductor package, a semiconductor chip is positioned in a space provided on a printed circuit board (PCB). The semiconductor chip is connected to the PCB via connectors in the part of the chip termed Ball Grid Array (BGA). The PCB provides the intra structure (such as vias, conducting planes including ground and power, wiring etc.) which enables the chip to communicate internally and externally to perform the functions for which it was designed.
In order to facilitate high speed and high performance operation a decoupling capacitor (also known as de-cap) is usually mounted on the PCB between the ground and power planes. The de-cap is required to suppress power/ground noise and provide components with stable power. However, the parasitic inductance associated with power distribution networks and mounting pads for de-caps are factors limiting the performance and effectiveness of de-caps. The parasitic inductance can cause unwanted resonance and when this occurs using de-caps may be more harmful than beneficial. The parasitic inductance is influenced by the location where de-caps are placed on the PCB. However, due to the complexity of high speed systems space on the PCB is at a premium. As a consequence, de-caps are usually not placed at the optimum locations on the PCB but rather at location where space is available. The practice of placing de-caps on the PCB where space is available tends to increase the length of the conductor which in turn increase the parasitic inductance. The problem is even exacerbated with BGA packages because the fan-out signals from the BGA make it almost impossible to place de-caps at optimum location on the PCB. The optimum locations would be those locations on the PCB where the parasitic impedance would be reduced. Even if the de-caps were to be placed at the optimum locations, they would not abate the vertical noise that is generated as a result of the parasitic inductance.